From past efforts over a number of years, we have established the capability to fabricate and implant an artificial heart and manage the recipient of the device over an extended period of time. Thromboresistant materials having long life in this application have been developed. Anatomical and functional system constraints are known. Control of the pneumatic driving system and operational characteristics are understood in detail. We therefore propose to combine and apply this information in order to study the physiology of an optimally designed device as total replacement of the heart in animals. Current artificial heart physiological studies have identified specific hemodynamic alterations, notably atrial pressure pulsatility and venous congestion. We attribute these alterations to inadequate inflow hemodynamics resultant from functional atrial volume restricton. The objectives of this proposed work are to complete the design of an optimal cardiac prosthesis, to evaluate the results of its implantation in calves, and to validate and refine a model of the atrial function as it affects the heart's performance. Series of in vitro and in vivo experiments are planned to measure the effect of varying physical characteristics of the heart's inflow on cardiac output, atrial pressure pulsatility, venous pressure, and other hemodynamic values. Cineangiography will be used for ascertaining the hemodynamic function of the heart's inflow in vivo. We anticipate that this work will add significantly to the progress towards a feasible total artificial heart.